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    <title>Document</title>
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    <script>
      /* 矩阵表格 */
      const arr = [
        [1, 2, 3], //0(0,1,2)
        [4, 5, 6], //1(0,1,2)
        [7, 8, 9], //2(0,1,2)
      ];
      /* for (let i = 0; i < arr.length; i++) {
        for (let j = 0; j < arr[i].length; j++) {
          console.log(arr[i][j]);
        }
      } */
      for (let v1 of arr) {
        for (let v2 of v1) {
          console.log(v2);
        }
      }
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